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clk: divider: fix calculation of initial best divider when rounding to closest 

Similar to the reasoning for the previous commit

	DIV_ROUND_CLOSEST(parent_rate, rate)

might not be the best integer divisor to get a good approximation for
rate from parent_rate (given the metric for CLK_DIVIDER_ROUND_CLOSEST).

For example assume a parent rate of 1000 Hz and a target rate of 700.
Using DIV_ROUND_CLOSEST the suggested divisor gets calculated to 1
resulting in a target rate of 1000 with a delta of 300 to the desired
rate. With choosing 2 as divisor however the resulting rate is 500 which
is nearer to 700.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Michael Turquette <mturquette@linaro.org>
hifive-unleashed-5.1
Uwe Kleine-König 2015-02-21 11:40:25 +01:00 committed by Michael Turquette
parent 26bac95aa8
commit 9315514252
1 changed files with 7 additions and 6 deletions
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13
drivers/clk/clk-divider.c
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@ -219,17 +219,18 @@ static int _div_round_closest(const struct clk_div_table *table,
unsigned long parent_rate, unsigned long rate,
unsigned long flags)
{
int up, down, div;
int up, down;
unsigned long up_rate, down_rate;
up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate);
up = DIV_ROUND_UP(parent_rate, rate);
down = parent_rate / rate;
if (flags & CLK_DIVIDER_POWER_OF_TWO) {
up = __roundup_pow_of_two(div);
down = __rounddown_pow_of_two(div);
up = __roundup_pow_of_two(up);
down = __rounddown_pow_of_two(down);
} else if (table) {
up = _round_up_table(table, div);
down = _round_down_table(table, div);
up = _round_up_table(table, up);
down = _round_down_table(table, down);
}
up_rate = DIV_ROUND_UP(parent_rate, up);